I stick to the recommended 500 calories a day on Fast days. My preferred pattern is two meals, lunch and supper, both 250 calories, but you may prefer one meal of 500, or three meals. Snacking is not recommended as the point of the Fast is to go considerable times without eating to rest the digestive system.
I have built up a repertoire of about 40 recipes, that I eat on fast days. I have googled '250 calorie meals' and this produced hundreds, which I scrolled through to find those I like, I have bought 5:2 recipe books and I have devised my own, by trimming down recipes I already use.
A lot of my recipes are based on chicken, fish plus lots of vegetables as main courses, cooked or as salads. Essentially it is a process of trial and error. For every recipe I have kept. several have been ditched. DH's opinion of spaghetti with kale pesto was unprintable. it went in the compost container and we had a salad instead.
On non-diet day, the best rule is be sensible but eat sparingly. Eat what you want but cut out the high calorie foods, boil rather than fry potatoes and do not put butter on them, don't eat between meals, fresh fruit rather than any kind of desert.
I lost 2 stone in 4 months about 4 years ago and I have kept it off.
